There can be many different explanations for the cause of the First World War. The immediate cause was the assassination of the Archduke Francis Ferdinand of Austria. This plunged European nations into the conflict that the United States entered a couple of years later. Yet, I think that such an event and the response that followed is the result of intertwining and concurrent realities that end up causing the conflict. The growth and emergence of nationalism and the expansion of borders to a point where love of one's nation became synonymous with the overtaking of another is one such element. Another would be the rise of militarism in European nations. The military in different European nations were beginning to occupy an important role in the affairs of the country, making aggressivism a part of this relationship with other nations. Secret alliances with other nations helped to plunge the entire continent into conflict as one member of the alliance was threatened. In the end, there were multiple causes to the conflict.

The causes of World War I, which began in central Europe in July 1914, included many intertwined factors, such as the conflicts and antagonisms of the four decades leading up to the war. Militarism, Alliance, Imperialism, and nationalism played major roles in the conflict as well. However, the immediate origins of the war lay in the decisions taken by statesmen and generals during the July Crisis of 1914, casus belli for which was the assassination of Archduke Franz Ferdinand of Austria by Gavrilo Pricip, an irredentist Serb.

I am reading a book right now by John Keegan about World War II. He discusses a little bit about the causes of World War I because the outcome of it was part of the cause of World War II. Keegan says that one reason Germany attacked France was because Germany was trying to acquire colonial empire and France, which already had a colonial empire was in its way.

J. F. C. Fuller was a British general who wrote a book about U.S. General Grant. In that book, Fuller says that one reason for World War I was the industrialization of Germany which made England feel that it would no longer be able to make so much money off of its industry.

Concerning America's entry into WW I on the side of England and France, I read a scholarly article when I was in college that pointed out that American financial institutions and business men had made a lot more prewar loans to British interests than to German interests.

Wars are always the result of many reasons. I have mentioned only three.